Underground mining machine



July 15 1924. 1,501,795

A. K. MITCHELL UNDERGROUND MINING MACHINE Filed Oct. 2, 19:22 13Sheets-Sheet l .S SN w N C P%| rv il mn .Q R Trw n l l L Mi, 1w 2 M 1U.V l u ce N rl m o Q D afi-m .WN WM. c m !,\\\U| e o I\| a 0 o O 0 n i@,a .I o b-No .o e .Q Nh. -I c mmm o uw i1 I MiN/ nw E n f I 1 x M n O 0Sw im 0%.@ D w Il w@ 41 July 15 1924.

A. K. MITCHELL UNDERGROUND MINING MACHINE Filed Oct. 2, 1932 13Sheets-Sheet 2 July 15, 1924. 1,501,795

A. K. MHTCHELL UNDERGROUND MINING MACHINE Filed oct. 2, 1922 13sheets-Sheet 3 C. WW

Mmm/ww Juy 15, 1924. 1.501,795

A. K. MITCHELL UNDERGROUND MINING MACHINE Filed Oct. 2, 1932 13Sheets-SheeiI 4 GWW July 15 l1924. 1,501,795

A. K. MITCHELL UNDERGROUND MINING MACHINE Filed Oct. 2, 19z2 13Sheets-Sheet 5 ,4H/w ff. Amm/1 CWM A. K. MITCHELL UNDERGROUND MININGMACHINE July 15, 1924.

vFiled Oct. 2, 1922 13 Sheets-Sheet 6 July 15, 1924. Y

A. K. MITCHELL UNDERGROUND MINING MACHINE Filed Oct. 2, 1922 13Sheets-Sheet '7 um, m

July 15 ,v 1924. 1,501,795

A. K. MITCHELL UNDERGROUND MINING MACHINE Filed Oct. 2, 1922 13Sheets-Sheet 5 3;, CWM@ July 15,1924. 1,501,795

A. K. MITCHELL UNDERGROUND MINING MACH-I NE Filed Oct. 2, 1922 13Sheets-Sheet 10 July 15 .'1924.

A. K. MITCHELL UNDERGROUND MINING-MACHINE Filed Oct. 2, 192:2 13Sheets-Sheet ll VME ATTORSE Y NHN vom, Nevn Nw E En SQN MSM mow on @nwm. Nhm

July 15 1924. v

- A. K. MITCHELL UNDERGROUND MINING MACHINE 13 Sheets-Sheet l2 FiledOct. 2

July 15, 1924.

A. K. MITCHELL UNDERGROUND MINING MACHINE Filed Oct. 2, 1922 13Sheets-Sheet l5 INVENTOR l 6 gg M ATT RNEY Patented July l5, 1924.

UNITED STATES 1,501,795 PATENT OFFICE.

ARTHUR K. MITCHELL, 0F BRONXVILLE, N EW YORK, ASSIGNOR '101 ST. JOSEPHLEAD COMPANY, OFNEW YORK, N. Y.,

A CORPORATION or NEW Yom.

UNDERGROUND MINING MACHINE.

Application led October 2, 1922. Serial No. 591,689.

T o all whom z't may concern.'

Be it known that I, ARTHUR K. MITCHELL, a citizen of the United States,and a resident of Bronxville, county of Westchester and State of NewYork, have invented certain newand useful Improvements in UndergroundMining Machines, of which the following is a specification.

This invention relates to Aan improved underground mining machine and isin part., a'continuation of my prior application for patent tiled July21st, 1920, Serial No. 397,881.

Generically considered, it is the primary object and purpose-of thisinvention to provide a machine of the above character which isespecially designed for operation in mine corridors of limitedheight,'and Which will be exceedingly mobile and can be readily operatedin a comparatively restricted space, as for instance, between the roofsupporting pillars, in the loading of the transporting vehicles withore.

It is another object of my invention to r provide an improved system ofcontrol enabling the operator Without changing his position upon themachine, to properly manipulate the ore collecting dipper or shovelandto position the same above the ore receiving and transportingvehicle, or to effect the bodily movement or travel of the machine.

The present invention also contemplates the provision of an improvedmounting for the dipper or shovel carrying boom and means for impartinga longitudinal forward thrust or retracting movementl to the boom sothat the shovel or clipper after being filled,lmay swing with thesuperstructure of the machine between spaced roof supporting pillars inthe mine corridor and thus dispose the shovel in a dumping position overthe ore receiving vehicle. y

In one practical embodimentof the invention I provide av rotatablesuperstructure mounted upon atractor'supported frame and alongitudinally traveling shovel-carrying boom carried by thesuperstructure. Three electric motors of the reversible type are mountedupon the superstructure and each connected in suitable electriccircuits, one of said motors operating the tractor actuating mechanismor the boom actuating mechanism, another of said motors actuating theboom hoisting means, while the third motor actuates the superstructurerotating means.- By the manipulation of suitable circuit controllingswitch levers, the operator may render one, or simultaneously two orthree, of the motors operative to effect the desired operation, each ofthe motors being preferably equipped with a magnetic brallie so thatwhen its circuit is broken, the operation of the motor is instantlystopped.

It is also one of the detailed objects of the invention to provide ampleautomatic means for breaking the circuit of the boom operating motor tolimit the forward thrusting movement and the retracting movementof theboom, and also to provide automatic circuit-breaking means Ifor thehoist motor to limit the elevated position of the shovel or dipper aswell as to stop the hoist motor, when during its lowering motion theshovel or dipper strikes the mine floor or other obstruction.

Another of the detail-objects of the invention is to provide simple andeicient means acting to positively lock ythe tractors against movementto hold the machine as a whole, in a st-ationary position While the boomand shovel are being operated to gather' and load the ore.

In accomplishing the aforementioned objects I have at the same timesucceeded in devising a machine primarily designed for undergroundmining operations which, in view of its manifold capabilities, is ofrelatively simple construction, light in weight, and wherein the variousoperating parts are compactly arranged and not liable to get out oforder.

With the above and other objects in view, the invention consists in theimproved form, construction and relative arrangement of the severalelements, as will be hereinafter more fully described,` illustrated inthe accompanying dra-Wings and subsequently incorporated in thesubjoined claims.

In the drawings wherein I have illustrated one practical embodiment ofthe invention and in which similar reference characters designatecorresponding parts throughout the several views,

Figure 1 is a top plan view of an underground mining machine,constructed m accordance with my present invention;

Figure 2 is a side elevation Aof the machine, the boom and shovel beingshown in full lines in its lowered retracted position A frame ;l

and in dash lines in the retracted elevated` tractor supported frame,the superstructure being removed; V

Figure 6 is a transverse section taken on the line 6-6, of Figure 1;

Figure 7 is a front end elevation of the tractor frame, the tractorsbeing shown in section; e

Figure 8 is a top plan view partly in section of the superstructuresupport-ing Figure 9 is an enlarged plan view with certain parts shownin section to more clearl illustrate the driving connection between tliemotors and the superstructure rotating mechanism and the tractoractuating mechanism;

Figure 10 is a sectional view through one of the motor brakes with partsthereof in elevation, taken on the line 1 0-10 of -Figure l;

Figure 11 is a section taken on the line 11-11 of Figure 10;

Figure 12 is an end elevation of the brake;

Figure 13 is a detailv sectional View through the brake engaging wheelon the shaft of the boom operating motor and illustrating the manuallyoperable clutch connection between said wheel and the boom operatinggearing;

Figure 14 is an enlarged detail section showing the universal connectionbetween the boom gudgeons and the carriage blocks mounted forlongitudinal movement on the superstructure of the/machine, said sectionbeing taken on the line 14-14 of Figure 1;

Figure 15 is a transverse section taken on the line 15-15 of Figure 1,showing the worm gear driving connections between the operating motorsand the hoisting drum and boom operating shaftrespectively; Figure 16 isa diagrammatic view showing the Fboom and shovel in full lines in thefully extended lowered position with relation to the machinesuperstructure and in broken lines in various other positions which theboom and shovelmay assume in the operations of hoisting and dumping thematerial.; Figure 17 is a diagrammatic View showing a conventionalwiring of the electric motor controlling circuits with the operatorscontrol levers and the automatic circuit breaking devices;

Figure 18 1s an enlarged detail plan view, partially diagrammaticillustrating the relation of its several control levers with respect tothe operators, seat;

lFigure 19 is an enlarged plan view showmaigres ing the actuating meansfor the forward and rear limit switches of the boom operating motor;

Figure 2() is a detail elevation of the actuating means for the forwardlimit switch;

Figure 21 is a section taken on the line 21--21 of Figure 19;

Figure 22 is a detail elevation of the lower limit, switch for thehoisting motor;

Figure 23 is a section taken on the line 23--23 of Figure 19;

Figure 24 is a detail elevation of the 0perating means for the rearlimit switch of the boom operating motor;

Figure 25 is a longitudinal sect-ion on the centre line of the dipper orshovel, which section intersects the shovel and boom head, to ether withthe latch device;

ligure 26 is a side view of the dipper or shovel and a longitudinalsection through one ofthe spring bumpers or shock absorbers; and

Figure 27 shows details of theA frame or bracket carrying the collectorshoes.

In the embodiment of the invention illustrated in the accompanyingdrawings as shown by Figs. 2, 3, 4; 5, 6, 7, and 8, the supporting frame5 for the tractor of the machine is of general rectangular form in planand includes a centrally elevated body portion 6 at each end of whichand at the opposite sides of the frame, the longitudinally extendingbearing supports 7 and 8, respectively, are formed. The frame extensions7 receive the bearings 9 for one end of the respective tractor drivingshafts 10 which are located at opposite ends of the frame 5. The innerends of the shafts 10 are journaled in suitable bearings provided in thelower portion of a housing 11, said housings being re-c spectivelysecured centrally to each end of the body 6 of the frame.

Upon the frame extensions 8 longitudinally adjustable bearings 12 aremounted in which shafts 13 are journaled. Any conventional means may beemployed for the purpose of adjusting the bearings 12 relative to theframe struct-ure.

At each side of the machine, the endless tractor treads 14 are engagedupon the sprocket wheels 16 and 17 secured respectively upon the outerends of the shafts 1C and 13 which project from each side of the machineframe. The fiexible tractor'treads between the spaced sprockets aresupported and guided by means of a plurality of flanged rollers 18suitably mounted upon spaced stud shafts fixed in each side of themachine frame. The tractor driving shafts 10 are actuated to propel theendl-ess flexible tractors in either direction by means of mechanismwhich will be presently described. y

Upon the'body portion 6 of the frame 5 an annular toothed rack 19 issecurely fixed in any preferred manner and within thisl ard 23 centrallyfixed therein, the lower end of said standard being engaged within anupwardly projecting boss 24 formed upon the frame bodyn. The latform 22is pro- -vided at its opposite si es with depending longitudinallyextending walls 25, said platform being also formed with an annulardepending flange 26 surrounding the rack 19, said ange merging into thewalls 25 at opposite sides of the superstructure` To the lower edge ofthe ange 26 a ring or annulus 27 is fixed and projects inwardly beneaththe lower edge of the rack 19 and thus prevents an oscillating movementof the rotatable superstructure withl respect to its axis. The meanswhereby this superstructure, together with the operating mechanismmounted thereon, may be rotated with respet to the tractor supportedframe 5, will also be fully disclosed in the subsequent description.

As shown by Figures 6 and 14, to the outer `face of each of thedepending walls 25 of the superstructure platform 22, a channel bar 28is secured by means of the bolts 29, saidbolts passing transverselythrough guide rails 30 which are secured upon the channel bar flanges inopposed relation to each other. The longitudinally extending ribs 31 ofthe guide rails 30 are engaged in suitable channels provided in thecarriage blocks 32 whereby said blocks may freely tralvel longitudinallybetween the guide rai s.

chain 33 are pivotally connected, a turn buckle 34 or other suitableslack take-up means being interposed in the length of this chain, asillustrated in Figure 2. The chains 33 engage with the sprockets 36mounted upon shafts suitably supported on the forward end of thesuperstructure, said chains being positively driven by the sprockets 37which,I are xed upon opposite ends of a transverse shaft 38 journaled insuitable bearings on the rear end of the platform 22.

The shovel or dipper carrying boom as herein illustrated, consists oftubular side members 39 whicli'are connected at their forward ends bymeans of 'ai boom head 40; Figures 1, 2, 3. The members 39 at their rearends are supported from the carriage blocks 32 inthe manner clearly`shown in To opposite sides of each carriage -block 32 the ends of alink type sprocket Figure 14 of the drawings, wherein it will be notedthat a gudgeon 41 extends transversely through eac-h boom member andprojects from one side thereof, said gudgeon being suitably fixed to theboom member as by means of the pin 42. The projecting end portion of thegudgeon 41 is reduced in diameter and tapered as at 43, said tapered endof the gudgeon being tightly dra-wn into the bore of a universallymovable socket member 44 shaped as a zone of a sphere, mounted in thecarriage block 32 by means of the nut 45 which is engaged upon thereduced threaded projection 46 of the tapered end 43 of the gudgeon.There are thus provided substantial connections between the boom membersand the traveling carriage blocks which allow a ,free vertical pivotingor rocking movement of said boom members relative to the carriage blockswhen the boom, together with the shovel or dipper carried thereby, is`hoisted or lowered with respect to the superstructure of the machine.Since these connections arel of the ball and socket type, the carriageblocks 32 cannot be subjected to any eccentric or torsional stresses dueto any side thrust on boom or dipper.

From the above it will be'seen thatthe means for projecting andretracting the boom consists of the sprocket chains 33 driven bythesprockets 37 and the carriage blocks 32 upon which the side arms ormembers 39 of the boom are mounted at their rear ends. This boomoperating means is actuated by a reversible motor to be hereinafterreferred to, andin certainv of the subjoined claims .I have includedthis motor or primary power source as an element sep arate Ifrom theboom operating means as above defined.

The dipper, bucket, shovel or skip, as it is variously termed, may be ofany suitable or preferred construction, in so far as the essentialfeatures of the present invention is concerned and it may be mountedupon the boom head in various ways. However, for purposes ofillustration I have herein shown the. shovel 47 as an open top scoop,Figures l, 2, 16, 25', and 26, pivotally `mounted for a tilting movementupon the trunnions 0r pins 48 fixed in the downwardly and forwardlyprojecting arms 49 of the boom head 40. Figure 25 is a centrallongitudinal section through shovel 47 and boom head 40. Thel shovel 'isso constructed and counterbalanced that when loaded with ore or other fwhen empty l'ies behind the pins 48; there-` fore, when free to tilt theempty shovel will return by gravity to its normal or digging position.Shovel 47 is held in this latter position by latch 401 which engages theupper end of lug 402. Latch 401 is held against rear end of shovel 47 bycompression of spiral spring 403 which is mounted on rod 404 in anannular recess'in boom head 40. To empty the loaded and elevated shovel,the operator presses down aipedal located conveniently near h'is feet,which motion overhauls a spring-actuated retrieving drum upon whichcable `405 is wrapped, causing cable 405 to pull lever 406 thusdisengaging latch 401, to which lever 406 is attached, from upper end oflug 402, thereby permitting shovel 47 to tilt forwardly and dischargeits load. TWhen the forward tilting movement is arrested, as hereafterdescribed, latch 410 engages the lower end of lug 402, thus holdingshovel 47 in position of maximum inclination so that its load of Ore maybe. completely discharged. Latch 410 is held against rear end of shovel47 by pres` sure of spring 403 through rod 404. An other pull on cable405 causes lever 406, through its connections with' latch 401 and rod404 to disengage latch 410 from lower end of lug 402, thus permittingthe empty shovel to tilt backwardly to its normal or digging position,such backward tilting being limited by the striking of buffers 411, ofwhich there is one on each side of the shovel, against arms 40.

Figure 26 is a side view of shovel 47 in its tilted position, showingalso a section through one of the two spring bumpers or shock absorbers407, but omitting details of the latch mechanism. The positions ofspring bumpers 407 are also shown by Figures 1, 2 and 3. When shovel 47is allowed to tilt forward to dump its load, its movement is arrested bythe engagement with lugs 409, of which there is one on each side of therear end of shovel 47, of hooked ends of plungers 408, said plungersacting under the impact to compress springs 412, thus absorbing theshock. Springs 412 are mounted within cylindrical members 407 which areattached to boom head. 40.

A shea-ve block 50 is suitably connected centrally to the boom head 40and around the sheave therein the cable 51 is engaged; Figures 1, 2 and3. This cable is trained over and supported by the spaced pulleys orsheaves 52 which are rotatably mounted upon a common axis 53 extendingbetween the upper ends of the standards 54,- said standards at theirlower ends being pivotally mounted as at 55 upon the superstructureplatform 22. The forward ends of longitudinally extensible rods 56 arealso loosely en gaged upon the pulley axis 53 at the outer side of eachpulley 52` said rods div/erging with respect to each other in a rearwardd 1- rection and being pivotally mounted at their rear ends as at 57.'These rods 56 may each be of the conventional sectional telescopicconstruction, suitable means, of course, being provided to securely holdthe rod sections in ixed relation to each other. rl`hus, when itisnecessary to propel the machine through a connecting passageway orcorridor .of very limited height, the standards 54 may be readily swungforwardly and downwardly to a lowered position as indicated by brokenlines in Figure 2 of the drawings.

Une strand of the cable 51 extends rearwardly and downwardly from one ofthe pulleys 52, and is suitably connected to the hoisting drum 58 whichis fixed upon. or integrally formed with a sleeve 59 loosely mountedupon the shaft 38 for independent rotation; Figures 9 and 15. The otherstrand of the cable 5.1 extends over a pulley or sheave l60 mounted inthe upwardly eX- tending arm of a bracket 61 which is provided forpivotal or rocking motion upon ,a shaft 62 for a purpose which will behereinafter explained. From this .sheave 60 the cable strand extendsrearwardly and is suitably attached at its end to the larger end of afusee drum 63 which is keyed or otherwise rigidly iixed upon the shaft38. The fuses drum 63 is so designed that the cable 51 will be unreeledfrom it at a variable rate such that when the dipper is being crowdedout by the operation of motor 69 as hereinafter described, starting withthe dipper lip on the plane of the tractor bottom, the path described bythe dipper will be horizontal. By reference to Figures 2 and 16 it willbe understood that the boom is projected, or crowded out an equaldistance for cach degree of revolution of shaft 38. As the boom andsheave 50 move out, if the lip of the flipper is to travel a horizontalpath on the plane of the tractor bottom, cable 51 must be unreeled at aprogressively increasing rate, which rate, since the cable is a two partone, must equal at any point twice the corresponding increment in thedistance between the points of Contact of the cable with sheaves 52 andsheave 51. A plain cylindrical drum, keyed to shaft 387 would unreel anequal length of cable for each degree of revolu tion of shaft 38 causingan outward and upward path of the dipper; therefore, a-

fusee drum designed as explained, is pro` vided. i

The sleeve 59' of the hoisting drum 58 has a worm gear 64 fixedv thereonwith the up per side of which a worm 65 on the shaft 67 of the hoistingmotor 66 is engaged; Figures 1, 9 and 15.- This worm and worm gear areenclosed Vwithin a suitable housing 68 mounted on the platform 22. Itwill thus be apparent that by the operation of the motor 66, thehoisting mechanism can be actuated to lift the boom and hoist the loadedshovel carried thereby/.to the desiredl height, while the'shovel is inits forwardly projected position, in its retracted position, or n anyintermediate position.

There is also mounted upon the superstructure platform 22, a secondelectric motor 69 which operates the boom thrusting and retractingmechanism and also the tractor propelling mechanism of the machine;Figures 1, 2, 4, 7 and 9. A third electric motor 70 mounted on theplatform 22 act'nates suitable gearing .cooperating with the fixed rack19 to rotate the superstructure upon the main frame 5. Each of thesemotors is of the reversible type and is equipped with a conventionalform of magnetic brake. These brakes I have indicated in theaccompanying drawings by the numerals 71, 72 and 73 respectively. I havealso illustrated one of the magnetic brakes in detail in Figures 10, 11and 12 of the drawings. It will suflice for the purpose of the presentexplanation to state that each brake includes opposed magneticallycontrolled brake shoes 74 which are adapted for friction-a1 brakingengagement upon opposite sides of a wheel 75 fixed in any suitablemanner upon the motor shaft. The brake shoes 74 normally en age wheel 75under the spring action, w ien, however, the magnet or solenoid coil isenergized, the shoes are magnetically pulled away from the wheel,against said spring action, thus releasing the brake for free operationof the motor.

Upon the end of the shaft of the motor 69 a clutch element 76 is looselyengaged, Figure 13, said element being fixed within one end of a sleeve77 which extends over one end of the hub portion 78 of the wheel 75. Afriction band is carried by the block 79 fixed to the wheel hub and isinterposed between the hub wall and the wall of the sleeve 77. .A springpressed wedge member 80 extends between spaced ends of the friction bandand acts to hold the same in tight frictional enuagement with the wallof the sleeve 7 7. ft will thus be apparent that there is obtained inthis manner a slip friction connection. between the clutch element 76and the wheel 75 which is fixed on the motor shaft. This device is desined to slip in the event of severe overloa s or sudden impacts, such aswould be caused .during forward crowding by the shovel striking animmovable obstruction. Motor 66, which operates the hoisting drum 58 isprovided with 4a similar device, as is motor 70, which operates theswinging mechanism, hereinafter described.

A manually shiftable complementary clutch element 81 is keyed upon theshaft 82 which is journaled in the upper part of a housing 83'enclosingthe worm gear 84 fixed on the shaft 38 and the worm 85 on said shaft 82which is engaged with the worm gear 84; Figures 1, 2, 9 and 13. It willthus be apparent that when the clutch element 81 is engaged with thecomplementary clutch element 76, rotation is transmitted from -the motorthrough shaft 82 and worm gearing 84 and 85 to the shaft 38 which drivesthe boom carrying chains 33 to move the boom in the desired directionand either thrust the shovel '47 forwardly to gather the ore therein orto retract the shovel, from which position it may be subsequentlyhoisted and disposed over the receiving and transporting vehicle. Theother end of the sha ft of the motor 69 is also provided with a clutchmember 86 with which a complementary clutch member 87 keyed upon theshaft 88 is adapted to co-act; Figures 1, 2 and 9. Between motor. 69 andsaid clutch elements there is also provided a slip friction device,similar to that previously described but not shown by the drawings.Shaft 88 is journaled in the upper end of a housing 89 and is providedwith a worm 90 which is engaged with the worm gear 91 on a transverselypositioned shaft 92 mounted in the housing walls,l Figure 6. Upon theinner end of this shaft a beveled gear 93 is fixed and meshes with asimilar gear 94 keyed upon a tubular shaft l95 mounted in the hollowstandard 23 fixed in the superstructure platform 22. The inner end ofshaft 92 is also journaled in one side of this standard. The lower endof the shaft 95 extends below standard 23 and has a beveled gear 96fixed thereon which is in mesh at diametrically opposite points with thegears 97 and 98, respectively, Figure 4. The gear 97,is keyed orotherwise fixed upon the end of a rearwardly extending shaft 99. The endof this shaft is suitably coupled at the rear side of the frame body 6to a shaft 100 j ournaled in the upper side of the housing 11 in whichthe inner end of the rear tractor operating shaft 10 is mounted. 100 isprovided with a worm 101 meshing with theworm gear 102 on the shaft 10.

The other gear 98 is loosely mounted-upon a forwardly extending shaft103 which, at the front side of the frame body 6, is suitably coupled toa shaft 104 journaled in the upper side of the housing 11 supporting theother tractor operating shaft 10. This shaft 104 is likewise providedwith a worm 105 meshing with the worm gear 106 on said tractor operatingshaft.

The shafts 99 and 103 are supported in suitable bearings adjacent to thegears 97 and 98 respectively, which are mounted in webs or hangers 107dependin from the frame body 6. A spider 108 1s arranged within thelower end of the boss 24 on the frame bodyV 6 and the upper ends of thearms of a yoke 109 are pivotally mounted in this spider, Fifrures 4 and6. lThe yoke arms are providedwith rollers 110 engaged The shaft inopposite sides of a peripheral groove formed in a double acting clutchcollar 111, said collar having clutch teeth on each of its side faces toengage with similar clutch teeth on the gears 97 and 98 respectively,and being mounted for longitudinal sliding but not for rotation upon endof shaft 103.. A bar 112 is swiveled at its ends in the lower ends ofthearms of the yoke 109 and to Jthis bar oppositely projecting aXiallymovable rods 113, are suitably connected, saidrods sliding throughsuitable bearing guides 114: in the hanger webs 107. Each of said rods113 at its other end is connected to a slide block 115 supported by theroller 116 mounted in a bracket plate 117 suitably fixed to the frame 5.Abell crank lever 118 is also fulcrumed in each of thcbracket plates117, one arm of the lever projecting upwardly and being operativelyconnected with a sliding locking clutch member 119 keyed upon the shaft99 or 103. These locking clutches are adapted to normally engage with afixed part 120 surrounding the shaft and depending from the fra-me body6 whereby said shafts 99 and 103 are locked against rotation. The. bellcrank levers are urged to this normal position by means of coil springs121 engaging the other or horizontal arms of said levers and interposedbetween said arms and the fixed parts 120, said springs also acting toyieldingly hold rollers 122 carried by the lever arms in the recesses orseats 123 provided in the upper surfaces of the slide blocks 115. I

Within the tubular shaft 95 a rod or shaft 124 is loosely mounted and isprovided at its upper end with a hand wheel 125 whereby said rod may beconveniently rotated, Figure 6. The lower end of this rod carries a pinor stud 126 eccentrically offset from the axis of the rod and engaged ina slot 128 provided in a connecting bridge 127 between the arms oftheyoke 109. It will thus be apparent that when this rod 124 is rotated,-

the pin 126 coacting with the walls of the slot 128 acts to shift theyoke 1.09 in one direction or the other, and thereby engage the clutchcollar 111 with the gear 97 or the gear 98, as the case maybe, and toalso simultaneously shift the rods 113 so as to actuate the bell cranklevers 118 and thereby y release the locking clutches 119 fromengagement with the parts 120. VVhenthe collar 111 is shifted to theleft from the position seen in Figure 6, it will be obvious that theshaft 103 is connected through the medium of said collar and the gear 97to the shaft 99 so that both shafts will rotate as a unit. Thus both ofthe flexible tractor treads will be driven in the same direction for astraight line movement of the machine. When the collar 111 is shifted inthe opposite direction and engaged with the gear 98, said gear is lockedtolthe shaft 103 so that rotation will be imparted to this shaft fromthe gear 96 in a direction oppositeto the direction of rotation of theother shaft 99. The tractor treads will thereby be moved in relativelyopposite directions so that the machine can be turned or manuvred in acomparatively. restricted space. 4

The clutches 81 and 87 are manually actuated to operatively connect themotor 69 to the 'boom operating gearing or to the tractor operatinggearing as the case may be, through the medium cfa lever 224 which ispivotally mounted upon one side of the gear housing 89, 'Figure 9. Thislever is provided with an upper arm 225 connected by the rod 226 to aswinging yoke 227 in which the shiftable clutch member 87 is carried.The lever 224 is also provided with a second arm 228 connected by thelink 22,9 to one end of a lever 230 which is fulcrumed intermediate ofits ends uponvthe superstructure platform 22, the other end of saidlever being connected by a rod 231 to the lower part of yoke 232,(Figure 2) which is so fulcrumed on platform 22 that its lower partengages the shiftable clutch element 81. As seen in. Figure 9, when thelever ismoved in one direction toward the center line of the machine,the clutch element 81 is thrown out to disconnect the motor from thegearing operating the boom while the other clutch element 87 is throwninto engagement with the clutch 86 to connect said motor to the gearingoperating the tractors. Upon shifting this lever away from the centerline of the machine, such condition is reversed and the motor isconnected in driving relation with the boom operating gearing anddisconnected from the tractor operating gearing.

The superstructure platform with the motors and mechanisms mountedthereon is rotated with relation to the' supporting frame 5, asindicated by the broken line shown in Figure 1, by means of the gearingillustrated in Figures 4 and 9 of the drawings, from reference to whichit will be noted that the shaft extension 134 from the motor 70 isprovided with a worm 135 meshing with the worm gear 136 on the upper endof a perpendicular shaft 137 mounted in suitable bearings on theplatform 22. A pinion 138 is fixed to the lower end of this shaft andmeshes with the gear 139 on the upper end of a second perpendicularshaft 140. The lower end of this shaft 140 is in turn provided with apinion 141 which directly engages with the teeth of the fixed annularrack 19 secured upon the frame. body 6. The upper face of this rack isobliquely inclined as at 142 and upon the same suitably spacedfrustro-conical rollers 1-'13 mounted in the platform 22 are engaged,

whereby the superstructure and the parts carried thereby will beadequately supported.

Each of the three collector rings 20 is connected with one phase of thethree phase alternating current circuit to which, by means of aninsulated three-wire cable, the tractor or truck, is wired. Each ofthese rings is normally engaged by a collector shoe 144 (a, Y), or c;Figures 17 and 27. The three collector shoes are mounted on a singlelibre, board 503, the spindles 512 of the shoes sliding loosely throughholes in board 503, and shoes 144 are pressed downwards by springs 502through which pass spindles 512. Each collector shoe 144 is kept inalignment with its collector ring 20 b v a toggle connection with libreboard 503. Fibre board 503 is rigidly mounted upon three bolts 508 whichpass upwardly with a sliding fit through holes in bracket 501 to a rigidconnection with plate 511, bracket 501 being bolted over a suitablylocated aperture in platform 22. Plate 511, bolts 508, libre board 503and collector shoes 144 a., Z), and c, are normally held down inposition in which rings 20 are engaged by shoes 144 by latch 504 whichis pivoted to bracket 501 by pin 509, a notch in latch 504 being pressedagainst the edge of a hole in plate 511 by leaf spring 505. Latch 504 isconnected by rod 160 with lever 152 which is conveniently located nearthe left hand of the operator, being pivotally connected at 510 withplatform`22. If the operator desires to disengage shoes 144 from rings20, he presses the upwardly projecting forward end of lever, 152 to hisleft, thus disengaging latch 504 from plate 511, permitting plate 507,bolts 508, fibre board 503, and shoes 144 to rise under the action ofspring 506, until shoes 144 are-lifted clear of rings 20 and all currentis thereby cut off from the circuits on platform 22. To re-engage shoes144 with rings 20, the operator presses downward on guard 507 attachedto plate 511, until notch in latch 504 snaps over edge of plate 511.

In Figure 17 I have diagramatically represented the various motors,brakes, switches, circuit breakers, cont-actors, and controllers,together with the circuits connecting them. There are three three-phasealternating current squirrel cage reversible motors, of a type, havinghigh resistance, high starting torque and low starting current. Eachmotor has two primary circuits, one for each directionof each motor, andeach of these circuits may be completed by means of double pole magnetswitches or contactors which are closed when their magnets are.energized by the manual closing of pilot or secondary circuits at thetwo master controllers, the central elements, or

levers, of which are indicated at 151 and 153.

If the operator desires to cause the boom and dipper to crowd out, hepushes lever 151 against Contact A, Figures 17 and 13. The followingsecondary circuit is thus completedz-from collector shoe 144", throughpoints 301, 302, 303, and 304to safety fuse 305, to closure betweencentral lever '151 of master controller and contact A, tio limit switch157 here assumed closed), through magnet coil 147c to point 306, throughcontacts of circuit breakers 307 and 308 to point 309, through point 310to collector shoe 144. Since vmagnet coil 147C is energized by thissecondary circuit, the main contacts 147 and 147 b are closed, thuscompleting the main circuit of motor 69 to canse forward mot-ion of boomand dipper. This main circuit is through solenoid coil of-circuitbreaker 308 to point 319, through closure of contacts 147b to point 320,through points 321 and 310 to collector shoe 144C. Regardless of anyswitch positions, terminal 322 of motor 69 is always connected throughpoints 323 and 301 with collector shoe 144". A circuit is simultaneouslyclosed from point 317 to terminal 324 of b rake 72 of motor 69, fromterminal 325 through point 326 to point 323, said points 317 an 323being on'main circuit of motor G9 previously outlined. Also, when magnetcoil 14,7c is energized, auxiliary contacts 147d are closed, thuscompleting the following secondary circuit: from collector shoe 144bthrough points 301, 302, 303 to 304, u

through closure of auxiliary' contacts 147d through point 327 to point328, through magnet coil 154, through points 329, 330 and 311 tocollector shoe 1441. Since magnet coil 154c is energized, the maincontacts 154a and 154b are closed, thus completing the Jfollowingcircuit: from collector shoe 144b throu h points 301 and 302 to point330, throug closure of contacts 154b to terminal 332 of brake 73 ofmotor 70,from terminal 333 through closure of contacts 154a to point331, through point 311 to collector shoe 1449-. From the above it isapparent that` the manual closure of lever 151 and contact A causescrowd motor 69 to operate in such a direction as to cause an outwardmotion of boom and dipper, and simultaneously energizes and thereforereleases magnet brake 72 of motor 69, thus permitting motor 69 tofunction, as well as also releasing magnet brake 73 of swing motor 7 0,thus permitting platform 22 to rotate slightly and relieve structuralstresses should the bucket receive a glancing thrust during

